I tried while making sure that there are no line breaks but without luck.
The problem seems to be that the variable are set just once?
I have modified the Ready to Install Dialog.sb8 example script to illustrate the problem and attached the script here.
As the example shows I have added %_SB_INSTALLDIR% to the value of %ADDITIONALINFO%
Testing the script gives the Install Folder dialog like this
Just hit <Next> and the Ready to Install dialog is shown as this
Now lets go <Back> and change the Destination Folder like this
Go <Next> and the Ready to Install dialog is shown as this
Please note that the runtime value %_SB_INSTALLDIR% is now represented with two different values. Also note that I not used any text resource in this example.